This invention relates to phonograph pickup cartridge attachments and more particularly relates to attachments capable of vibration damping and static removing.
The phonograph pickup cartridge industry has long sought a economical and reliable device which could simultaneously damp unwanted vibrations of the cartridge body and remove unwanted static electricity from the surface of a phonograph record disc. Damping devices for phonograph cartridges or tone arms have been devised in the past, but each has exhibited deficiencies which have limited its overall usefulness. Two such devices are illustrated in U.S. Pat. No. 2,754,372 (Weathers--July 10, 1956) and U.S. Pat. No. 3,301,565 (Bachman--January 31, 1967). The Weathers Patent describes a brush which is rigidly attached to a phonograph pickup cartridge body and which does not effectively engage the grooves of a record, but rather rides along the record surface. The Bachman Patent describes a resilient pad which is attached to the head of a tone arm through a pivot arm so that the cushion can move in a vertical direction with respect to a recording disc surface. A layer of viscous lubricant is placed between the tone arm and pivot arm to provide viscous damping. Both Weathers and Bachman teach that substantially more force should be applied to the brush or pad than to the stylus of the pickup cartridge. It has been discovered that this technique leads to unfortunate results when applied to modern record discs having variable pitch grooves. Since the brush or pad must ride in advance of the stylus, the pitch of the grooves acting on the pad or brush may be different from the pitch of the groove engaging the stylus. As a result, the brush or pad tends to bias the stylus out of the center of the groove it is engaging. This results in a tracking force which is excessive against one side of the groove and insufficient against the opposite side of the groove.
Another approach to tone arm or cartridge damping was suggested by A. R. Rangabe in a paper entitled "A New Method of Arm-Cartridge Damping", presented at a meeting in London, England in March, 1975. Rangabe suggests a cylindrical cup with a bottom surface defining a large radius of curvature which rides on a record adjacent a pickup cartridge stylus. The cup is partly filled with a high viscosity silicone fluid and is arranged coaxially around a spigot which is immersed in the fluid. A highly compliant rubber diaphragm is bonded to the cup and the spigot. Although Rangabe teaches that the force on the cup should be less than the force on the stylus, he suggests no means for damping vibrations parallel to the surface of the record and provides no means for removing static electricity from the recording disc. The Rangabe arrangement inherently generates vibrations which are picked up by the stylus, thereby creating "needle talk" of the type referred to in the March, 1975 Rangabe paper. In an attempt to reduce the "needle talk", Rangabe uses a lubricant on the bottom of the cup. The lubricant must be periodically replaced and only partially reduces the "needle talk".
Accordingly, it is a primary object of the present invention to provide an attachment for damping vibrations of a phonograph cartridge body occurring both perpendicular and/or parallel to the surface of a rotating phonograph recording disc having grooves engaged by a stylus which is supported by the body.
Another object of the present invention is to provide an attachment of the foregoing type which also removes static electricity from the grooves of a recording disc, as well as the surface of the disc.
Still another object of the present invention is to provide an attachment of the foregoing type which does not bias the stylus out of the center of the groove the stylus is engaging.
Yet another object is to provide an attachment of the foregoing type in which vibrations of a phonograph cartridge body perpendicular to the surface of the recording disc are damped by a substantially constant mechanical resistance.
Still another object is to provide an attachment of the foregoing type which minimizes "needle talk" of the type described by Rangabe.